Non-melanin pigmentation: A narrative review

Skin colour is determined by four biochromes: oxyhaemoglobin (red), reduced haemoglobin (blue), carotenoids (yellow), and, most importantly, the amount and type of melanin produced and its distribution in the skin. Pigmentary disorders comprise hypopigmentary, hyperpigmentary, and non-melanin pigmentary diseases. While the former two are discussed frequently, non-melanin pigmentary conditions are not unusual. Based on the aetiology and colour of pigmentation, these disorders can be categorised into blue-coloured lesions, hypopigmented lesions due to vascular aetiology, yellow-coloured lesions (xanthoderma), green-coloured lesions, pigmentation caused by heavy metals, and the miscellaneous group comprising conditions like chromhidrosis and ochronosis. While a few of these conditions may be confined to the skin, others can give an important clue to an underlying systemic disease. This review attempts to summarise the conditions that present as non-melanin pigmentation. It is imperative to recognise these entities and provide appropriate treatment to the patient.